Mie-Resonant Nanophotonic-Enhancement of Asymmetry in Sodium Chlorate Chiral Crystallization.

Studies on chiral spectroscopy have recently demonstrated strong enhancement of chiral light-matter interaction in the chiral near-field of Mie resonance in high-refractive-index dielectric nanostructures by studies on chiral spectroscopy. This situation has motivated researchers to demonstrate effective chiral photosynthesis under a chiral near-field beyond circularly polarized light (CPL) as a chiral source. However, the effectivity of the chiral near-field of Mie resonance for chiral photosynthesis has not been clearly demonstrated. One major challenge is the experimental difficulty in evaluating enantiomeric excess of a trace amount of chiral products synthesized in the near-field. Here, by adopting sodium chlorate chiral crystallization as a phenomenon that includes both synthesis and the amplification of chiral products, we show that crystallization on a Mie-resonant silicon metasurface excited by CPL yields a statistically significant large crystal enantiomeric excess of ∼18%, which cannot be achieved merely by CPL. This result provides implications for efficient chiral photosynthesis in a chiral near-field.

Hydrogenation of silicon-nanocrystals-embedded silicon oxide passivating contacts.

We investigate the effect of hydrogen passivation of dangling bonds in silicon oxide passivating contacts with embedded silicon nanocrystals (NAnocrystalline Transport path in Ultra-thin dielectrics for REinforced passivation contact, NATURE contact). We first investigated the differences in electrical properties of the samples after hydrogen gas annealing and hydrogen plasma treatment (HPT). The results show that the NATURE contact was efficiently passivated by hydrogen after HPT owing to the introduction of hydrogen radicals into the structure. Furthermore, we examined the dependence of process parameters such as HPT temperature, duration, and H2pressure, on the electrical properties and hydrogen depth profiles. As a result, HPT at 500 °C, 15 min, and 0.5 Torr resulted in a large amount of hydrogen inside the NATURE contact and the highest implied open-circuit voltage of 724 mV. Contact resistivity and surface roughness hardly increased when HPT was performed under the optimized condition, which only improved the passivation performance without deteriorating the electron transport properties of the NATURE contact.

Fabrication of light trapping structures specialized for near-infrared light by nanoimprinting for the application to thin crystalline silicon solar cells.

Vehicle-integrated photovoltaics (VIPV) are gaining attention to realize a decarbonized society in the future, and the specifications for solar cells used in VIPV are predicated on a low cost, high efficiency, and the ability to be applied to curved surfaces. One way to meet these requirements is to make the silicon substrate thinner. However, thinner substrates result in lower near-infrared light absorption and lower efficiency. To increase light absorption, light trapping structures (LTSs) can be implemented. However, conventional alkali etched pyramid textures are not specialized for near-infrared light and are insufficient to improve near-infrared light absorption. Therefore, in this study, as an alternative to alkaline etching, we employed a nanoimprinting method that can easily fabricate submicron-sized LTSs on solar cells over a large area. In addition, as a master mold fabrication method with submicron-sized patterns, silica colloidal lithography was adopted. As a result, by controlling silica coverage, diameter of silica particles (D), and etching time (tet), the density, height, and size of LTSs could be controlled. At the silica coverage of 40%, D = 800 nm, and tet = 5 min, the reduction of reflectance below 65% at 1100 nm and the theoretical short-circuit current gain of 1.55 mA/cm2 was achieved.

Bayesian optimization of hydrogen plasma treatment in silicon quantum dot multilayer and application to solar cells.

Silicon quantum dot multilayer (Si-QDML) is a promising material for a light absorber of all silicon tandem solar cells due to tunable bandgap energy in a wide range depending on the silicon quantum dot (Si-QD) size, which is possible to overcome the Shockley-Queisser limit. Since solar cell performance is degenerated by carrier recombination through dangling bonds (DBs) in Si-QDML, hydrogen termination of DBs is crucial. Hydrogen plasma treatment (HPT) is one of the methods to introduce hydrogen into Si-QDML. However, HPT has a large number of process parameters. In this study, we employed Bayesian optimization (BO) for the efficient survey of HPT process parameters. Photosensitivity (PS) was adopted as the indicator to be maximized in BO. PS (σp/σd) was calculated as the ratio of photoconductivity (σp) and dark conductivity (σd) of Si-QDML, which allowed the evaluation of important electrical characteristics in solar cells easily without fabricating process-intensive devices. 40-period layers for Si-QDML were prepared by plasma-enhanced chemical vapor deposition method and post-annealing onto quartz substrates. Ten samples were prepared by HPT under random conditions as initial data for BO. By repeating calculations and experiments, the PS was successfully improved from 22.7 to 347.2 with a small number of experiments. In addition, Si-QD solar cells were fabricated with optimized HPT process parameters; open-circuit voltage (VOC) and fill factor (FF) values of 689 mV and 0.67, respectively, were achieved. These values are the highest for this type of device, which were achieved through an unprecedented attempt to combine HPT and BO. These results prove that BO is effective in accelerating the optimization of practical process parameters in a multidimensional parameter space, even for novel indicators such as PS.

Zn1-xGexOy Passivating Interlayers for BaSi2 Thin-Film Solar Cells.

BaSi2 is a promising absorber material for next-generation thin-film solar cells (TFSCs). For high-efficiency TFSCs, a suitable interlayer should be found for every light absorber. However, such an interlayer has not been studied for BaSi2. In this study, we investigated amorphous Zn1-xGexOy films as interlayers for BaSi2. The Zn/Ge atomic ratio in the Zn1-xGexOy film and the optical band gap depend on the substrate temperature during sputtering deposition. A suitable i-Zn1-xGexOy/BaSi2 heterointerface with spike-type conduction band offset was achieved when Zn1-xGexOy was deposited on BaSi2 at 50 °C. Furthermore, photoresponsivity measurements revealed that Zn1-xGexOy has an excellent surface passivation effect on BaSi2. When the thickness of Zn1-xGexOy was 2 nm, a high photoresponsivity of 0.9 A/W was obtained for a 500 nm thick BaSi2 layer at a wavelength of 780 nm under an applied bias voltage of 0.5 V between the front and rear electrodes, where the photoresponsivity in the short-wavelength region was significantly improved compared with that of BaSi2 capped with an amorphous Si layer. X-ray photoelectron spectroscopy revealed that the Zn1-xGexOy films suppressed the oxidation of the BaSi2 surface, decreasing the carrier recombination rate. This is the first demonstration of passivation interlayers for BaSi2 with suitable band alignment for carrier transport and surface passivation effects.

Effect of the Niobium-Doped Titanium Oxide Thickness and Thermal Oxide Layer for Silicon Quantum Dot Solar Cells as a Dopant-Blocking Layer.

Silicon quantum dot (Si-QD) embedded in amorphous silicon oxide is used for p-i-n solar cell on quartz substrate as a photogeneration layer. To suppress diffusion of phosphorus from an n-type layer to a Si-QD photogeneration layer, niobium-doped titanium oxide (TiOx:Nb) is adopted. Hydrofluoric acid treatment is carried out for a part of the samples to remove the thermal oxide layer in the interface of TiOx:Nb/n-type layer. The thermal oxide acts as a photo-generated carrier-blocking layer. Solar cell properties using 10-nm-thick TiOx:Nb without the thermal oxide are better than those with the thermal oxide, notably short circuit current density is improved up to 1.89 mA/cm2. The photo-generated carrier occurs in Si-QD with quantum confinement effect. The 10-nm-thick TiOx:Nb with the thermal oxide layer effectively blocks P; however, P-diffusion is not completely suppressed by the 10-nm-thick TiOx:Nb without the thermal oxide. These results indicate that the total thickness of TiOx:Nb and thermal oxide layer influence the P-blocking effect. To achieve the further improvement of Si-QD solar cell, over 10-nm-thick TiOx:Nb is needed.

Silicon Nanowire Heterojunction Solar Cells with an Al2O3 Passivation Film Fabricated by Atomic Layer Deposition.

Silicon nanowires (SiNWs) show a great potential for energy applications because of the optical confinement effect, which enables the fabrication of highly efficient and thin crystalline silicon (c-Si) solar cells. Since a 10-µm-long SiNW array can absorb sufficient solar light less than 1200 nm, the 10-µm-long SiNW was fabricated on Si wafer to eliminate the influence of the Si wafer. On the other hand, Surface passivation of the SiNWs is a crucial problem that needs to be solved to reduce surface recombination and enable the application of SiNWs to c-Si solar cells. In this study, aluminum oxide (Al2O3) was fabricated by atomic layer deposition for the passivation of dangling bonds. However, owing to a complete covering of the SiNWs with Al2O3, the carriers could not move to the external circuit. Therefore, chemical-mechanical polishing was performed to uniformly remove the oxide from the top of the SiNWs. A heterojunction solar cell with an efficiency of 1.6% was successfully fabricated using amorphous silicon (a-Si). The internal quantum efficiencies (IQE) of the SiNW and c-Si solar cells were discussed. In the wavelength region below 340 nm, the IQE of the SiNW solar cell is higher than that of the c-Si device, which results in an increase of the absorption of the SiNW cells, suggesting that SiNWs are promising for crystalline-silicon thinning.

Extracellular ATP inhibits IL-1-induced MMP-1 expression through the action of CD39/nucleotidase triphosphate dephosphorylase-1 on human gingival fibroblasts.

Extracellular adenosine triphosphate (ATP) is sequentially dephosphorylated by two ectoenzymes: CD39/nucleotidase triphosphate dephosphorylase (ENTPD) and CD73/5'-ectonucleotidase (5'-NT). Adenosine, its notable metabolite, may elicit potent anti-inflammatory responses. We examined whether the CD39-adenosinergic axis may exist in gingival fibroblasts and have an effect on the expression of matrix metalloproteinase (MMP)-1, the excess production of which leads to pathological matrix degradation. We showed that transcripts of CD39, CD73, and adenosine receptors A1, A2a, and A2b, but not A3, were expressed by human gingival fibroblasts by RT-PCR. We also identified the expression of CD39 in fibroblastic cells in rat gingiva by immunohistochemistry. ATP inhibited the expression of MMP-1 triggered by interleukin-1 at gene and protein levels. However, ATP-γS, a stable ATP analog, did not. The ATP-mediated MMP-1 inhibition was restored in the presence of POM-1, a specific ENTPD inhibitor, suggesting that CD39/ENTPD was involved in the MMP-1 inhibition. ATP metabolites including adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP), and adenosine inhibited MMP-1 expression, but ADP-ßS, a stable ADP, did not, suggesting that adenosine converted from ATP by the action of CD39/ENTPD and CD73/5'-NT may contribute to MMP-1 inhibition. Adenosine-mediated MMP-1 inhibition was restored in the presence of H89, a protein kinase A (PKA) inhibitor. Conversely, forskolin, an enhancer of intracellular cAMP, mimicked the effect of adenosine, suggesting that the cAMP/PKA signaling pathway is involved in adenosine-mediated MMP-1 inhibition. The present findings suggest the existence of an endogenous anti-tissue destructive mechanism in gingival tissue via the CD39-adenosinergic axis.

Extracellular ß-NAD(+) inhibits interleukin-1-induced matrix metalloproteinase-1 and -3 expression on human gingival fibroblasts.

There is increasing evidence to show that extracellular ß-nicotinamide adenine dinucleotide (ß-NAD(+)) modulates various biological functions in inflammatory/immune regions. The aim of this study was to determine the effect of ß-NAD(+) on matrix metalloproteinase (MMP) expression on human gingival fibroblasts (hGF), the excess production of which leads to the matrix degradation associated with the pathological processes of periodontitis. The expression of MMP-1 and MMP-3 on hGF was determined by real-time polymerase chain reaction (PCR) and an enzyme-linked immunosorbent assay. The phosphorylated status of mitogen-activated protein (MAP) kinases, extracellular signal-regulated kinase 1/2 (ERK), c-Jun N-terminal kinase (JNK), and p38 and the expression of inhibitor κB (IκB)α were determined by Western blotting. ß-NAD(+) inhibited the expression of MMP-1 and MMP-3 triggered by IL-1α at gene and protein levels. ß-NAD(+) had no significant effect on the IL-1α-induced phosphorylation of ERK1/2, JNK, and p38 and also had no effect on the IL-1α-induced degradation of IκBα relative to the control, suggesting that inhibition by ß-NAD(+) was independent of the MAP kinase and the nuclear factor-κB signaling pathways. Transcripts of NAD(+)-metabolizing enzymes, such as NAD(+)-glycohydrolase, adenosine diphosphate (ADP)-ribosylcyclase, and ADP-ribosyltransferase, were expressed by hGF as assessed by RT-PCR. Experiments using α-NAD(+), which is not a substrate for ADP-ribosylcyclase or ADP-ribosyltransferase, revealed the possible contribution of NAD(+)-glycohydrolase to the inhibition of MMP. This is consistent with the finding that ADP-ribose, an NAD(+)-metabolite by NAD(+)-glycohydrolase, exhibited MMP inhibition similar to ß-NAD(+). The present findings may provide an additional viewpoint to clarify a natural feedback mechanism during the inflammatory process in periodontal tissue.

Why do chronic subdural hematomas continue to grow slowly and not coagulate? Role of thrombomodulin in the mechanism.

OBJECT: Thrombomodulin is a thrombin receptor on vascular endothelial cells that is highly expressed when these cells are injured, and it has anticoagulating activity. The authors investigated thrombomodulin expression to clarify why chronic subdural hematomas (CSDHs) continue to grow slowly, like a tumor, and are liquefied. METHODS: Burr hole craniotomy and drainage were performed in all 35 patients with CSDH who were included in the study. The plasma-soluble thrombomodulin and blood clotting factor values were determined in the hematoma and in peripheral blood. In the seven most recent cases, the plasma-soluble thrombomodulin values were determined in the residual hematoma collected from the drainage tube the day after surgery. The outer membranes of the CSDH that were obtained as specimens at operation were stained with monoclonal antibody against thrombomodulin for immunohistochemical studies. The plasma-soluble thrombomodulin values were higher (p < 0.0001), and conversely the values for factors V and VIII were lower in the hematoma than in peripheral blood (p < 0.0001). The plasma-soluble thrombomodulin values were lower in the residual hematomas than in the same lesions at operation (p = 0.018). The endothelial cells on the sinusoidal vessels exhibited immunoreactivity with thrombomodulin antibody in 28 (93%) of 30 cases. CONCLUSIONS: The thrombomodulin is expressed on the sinusoidal vessels, and the blood coagulation system is inhibited in the hematoma. These findings indicate that these vessels are continuously injured and fail to heal. As a result, the bleeding from the sinusoidal vessels may persist, and the hematoma may grow slowly and fail to coagulate. It is suspected that transmitted pulsation variations in the hematoma cavity generate sinusoidal vessel injury.